class Cat:
    def shout(self):
        print("喵")


class Dog:
    def shout(self):
        print("汪")


def shout(obj):
    obj.shout()


cat = Cat()
dog = Dog()
shout(cat)
shout(dog)

calculator = Calculator(10)
print(calculator + 5)
print(calculator - 5)
print(calculator * 5)
print(calculator / 5)


class Calculator(object):
    def __init__(self, number):
        self.number = number

    def __add__(self, other):
        self.number = self.number + other
        return self.number

    def __sub__(self, other):
        self.number = self.number - other
        return self.number

    def __mul__(self, other):
        self.number = self.number*other
        return self.number

    def __truediv__(self, other):
        self.number = self.number/other
        return self.number
